Stroboscopic system



May 23, 1933. BRoADwELL 1,910,982

STROBOSGOPIC SYSTEM Filed April 17, 1930 2 Sheets-Sheet 1 lNVE/VTUR H.BROADWELL '0 I I A ATTORNEY y 3, 1933. H. BROADWELL 1,910,982

" STROBOSCOPIC SYSTEM Filed April 17, 1930 2 Sheets-Sheet 2 FIG. 4

SECONDS P01. 55 NUMBERS PULSES //v 056F555 lNVENTUR H. BROADWELLtelephone dials.

patented May 23, i

j; n UN ED STATES PATENT/OFFICE nownnfo nRoAnwELL, on RIDGEWOOD, NEWJEB$EY,I nssieivon To ELL TELEPHO LABORATORIES, INCORPORATED, OF NEWYORK This invention relates to systems for determining variations in thespeed of rotating bodies and more particularly to stroboscopic systemsfor observing speed variations in 'The present invention is applicableinsubstantially all situations Where it may be desirable or necessary,to make determinations as to the speed or rate of travel of devicescharacterized by some form of periodic I110- tion. a The embodimentelected by applicant for illustrating the invention, discloses astroboscopic system :employed to determine Whetherithe speedof operationof an impulse transmitting device, such as a telephone dial, is. Withinthe maximum and minimum speed limitsrequired for the proper operation oftelephone automatic switching apparatus controlled thereby. It is notintended, however, that the invention. be limited to this particularadaptation. v

Automaticswitches asemployed in telephone exchanges are designed tofunction accurately when the actuating or controlling impulses arereceived at a rate which is maintained within certain narrow limits. Inorder'to insure the transmission of impulses Within these limits," it isobviously necessary that the impulse transmitting mechanism should be sodesigned as to guarantee theproper rate of transmitted pulses. v i

In Patent1,160,356, issued to A. H. 'Adams on November 16,1915, thereare disclosedanddescribed a method and means for checking and adjustingthe speed of rotation of impulse transmitters whereby it may bedetermined whether or not thetransmitter or dial is functioning atapredetermined rate necessary to transmit pulses within the limits setfor theproper functioning of automatic telephone switches. This patentproposes the use of an indicator card provided on its face with seriesof circumferentially arranged printed or 3 stamped projections, whichmay be observed through shutters associated with the tines ofa tuningfork. Though the system di closed in this patent readily permits avisible=record to be made of variations in dial speedbeyond set limits,it depends for its set maximum and minimum limits.

YORK, Y., A CORPORATION .OFNEW s'rnonoscorrc sYs'rnn Application filedApril 17,

1930. Serial No. 445,182. i i

accuracy'upoii the theory that a dial so ob served, operates at aconstant speed, that is, that the-dial willbe traveling at the samespeed of rotation throughout its entire travel. a e e That there is avariation in the speed of rotation of a dial during a single operationthereof, is wellknowmand hasbee n ob served andrecorded by variousmethods of test. It is apparent therefore, that a system for checkingthespeed offlrotation of a rotating body such; as a spring controlledtelephone dial, which does not operate at a constan'tspeed throughoutits travel, should be suclizasjto compensate for this speed variation"in order that the results obtained stroboscopicallymay be an accuratepicture ofthe Workings of the dial and a true record of thedial speedvariations within certain It is therefore an object of this invention toprovide an improved stroboscopicsystem whereby variations inithe speedof rotation of a rotating "bodyliaving a non-uniform speed.characteristic may be accurately ob'- served;

This object is attained in accordance with a feature of the invention bytheprovisijon.

of an indicator card or stroboscopic target on the" face of which isimpressed aseries of indications, the space occupled by each ofWhichhaving been determined fromthe speed characteristic of the rotatingbody to be tested. v

The invention will be {readily understood from the "following detaileddescription made with reference to the accompanying drawings whichinclude curves employed in calculating the indicator card or target.

F 1g. 1 shows in perspective, the manner in which the improved methodand apparatus embodying the features of this invention may be utilized;

Fig. 2 is a view [of a attained in accordan hereinafter described; Fig.3 isfla view of atelephone dial and the target adapter employed inmounting the targetfon the dial;

Fig. 4 is agraphic representation showing the relation between pulsenumber and the stroboscopic target, e with the method to be averagepulse value in seconds of a certain lot of dials;

Fig. 5 is a graphic representation showing how the width of each targetindication is obtained; and

Fig. 6 is a view of a target in'the making and discloses the method bywhich the indications are laid out thereon.

The following description is directed in detail to the method employedin obtainin an indicator card, for use in connection wit a vibratingtuning fork or an interrupted light source, the indications impressedthereon being so positioned on the indicator and of such size that thenumber thereof per second, visible when viewed through a vibratingtuning fork or by means of an interrupted light source at any particularpoint in the revolution, is proportional to the instantaneous speed ofthe rotating body at that point.

The method to be described for computing the spacings on the indicatoror target, is particularly desirable when a great number of dials haveto be tested and an average computation oftheir speed characteristics isessential. However, it is to be understood that the speedcharacteristics of each dial to be checked could be determined and anindicator designed accordingly. This obviously is impractical, as itwould necessitate the calculation of an indicator card for each dial,and when dials by the thousands are to be checked, such individualcalculations would be prohibitive. An averageindicator card calculatedby observing a number of dials over an extended period of time has beenfound to be satisfactory and truly representative for the checking ofall dials.

Applicant has elected, to describe in detail the exact procedurefollowed in obtaining an average indicator card and accordingly, hasresorted to the use of specific data obtained during an exhaustive studyof dial operations.

Pulse rate data may be obtained by observing a number of dials and thetime for each pulse taken over a period of years. From this data may becalculated the average time consumed by each pulse, and a grand averageof the total average pulse determined. Such data is shown in thefollowing Table #1.

Table #1 Pulses 1 2 3 4 5 6 7 8 9 Average ...0985 0995.1013 10171033.1050 1062.1075 1093 Grand average of the nine pulses=.1035

Table #2 Pulse 1 2 3 4 5 Dev 00476 00420 00318 00180 0028 7 Pulse 6 7 89 Dev. 00124 00276 00428 00584 These deviations from the average valueare then expressed as percentages, and this percentage Average pulsedeviation Grand average pulse value is employed as a factor which isused in the computation of the indicator for various dial speeds such as8.0 pps., 9.5 pps. etc. The new deviations thus obtained, when addedalgebraically to the time of one pulse at the new average rate beingconsidered, say 8.0 pulses per second, gives the actual time (t) of thatparticular pulse:

For example, I 1

Pulse #1 at 8.0 pps. (pulses per second) in the case in considerationequals 50.)

360 E 1/12 Then H D where D and N- (one pulse representing 1/12revolution, since the dialis laid out on a 30 degree basis.)

Substituting and reducing, H degree. From this formula, afterdetermining (t) for each pulse, as shown above, the corresponding anglesH can be directly computed. Thus for #1 pulse atthe average or nominalrate of 8.0 pps.,

A smooth curve of H versus pulsenumber is then plottedto large scale,the. first. pulse number being indicated on the curve as starting atzero-degrees, and thej succeeding pulse numbers beingshown thirty;degrees apart. (See Fig. 5.) it

At the zero degre'eor first pulse position, the width of the firstdivision on the target is taken directly from the curve (Fig.6), and inthe case considered, thisgvalue equals 5.031 degrees. This division islaid inhorizontally on thegraph (Fig. 5) ,ywith its center on thezerocenterline. The end 1of this division therefore .standsat. half thisdistance, or 2516 degrees from the zero position. The end of the-seconddivision will stand at approximately 2.5l6+5.031 or 7.547 degrees,ignoring forthe moment'the effect of the drop of the curve. Plotting ina vertical line through point .7 .547 degrees, a horizontal linerepresenting the second division is drawnwith its midpoint passingthrough the curve. The height of this line measured from the base line,or 5.029 degrees is then the length of this division to three decimalplaces. Succeeding divisions are determined in the same manner, steppingalong the curve as described below until the full pulse range of thedial is covered.

One half the length of the first division of 2.516, plus the true lengthof the second division or 5.029 equal 7.545 degrees, which is thedistance from the zero position at which the end of the second divisionwill be located. In like manner the end of the third division will belocated from the zero position a distance equal to 7.545 plus the truelength of the third division as read from the curve (5.026 degrees) or12.571 degrees. These computations are continued andthe values 2.516,7.545, 12.571 etc. or tabulated. This data is then laid out accuratelyto large scale and the spaces divided in two, one half being filled inblack and the other left white.

From the foregoing it is evident that the exact length of each divisionthroughout the entire range of the dial may be read from the curve, andit will be noticed that instead of each division being of the samelength (5.031 degrees), as would be the case should the dial operate atan exactly uniform speed of rotation, each succeeding division issmaller as accounted for by the drop in the curve.

A reference line X on the indicator card (Fig. 6) is 110w chosen and thedivisions, as determined above, drawn in. The first whole division(5.031 degrees) will be bisected by thereferenceline, a black division(2,516 degrees) lying on one side of; the

reference line and a white division (2.516 degrees) lying on theopposite side. The

i 7 end of the next black division will then be or 5.030 de rees fromthe reference line and the end of the succeeding white division2.516+5.029 or 7.545 degrees from the reference line. The indicatorcard, or stroboscopic target may contain as many circumferentiallyplotted series of divisions as are found desirable, though two rows havebeen found to be the most practical.

Thetarget shown in the drawing Fig. 2, discloses two series of divisionsone plotted for the minimum dial speed (eight pulses per second) and theother for the maximum dial speed (eleven pulses per second).

It is evident from the foregoing description that applicant has deviseda stroboscopic ,target, the indications of which, to be viewed through avibrating tuning fork, or by means of an interrupted light source aredesi ned as tosize and location on tar et in. accordance with the speedcharacteristic oftherotating body with which it is to be used. It isequallyapparentthat a rotating body equipped with a target of thisdesign may be more accurately and more read-,

ilystudied and itsvariations in speed of rotation from certain setlimits more precisely determined. i 1

Referring. now. to. Figs. 1, 2 and 3, the target which in itselfconsists of a thin relatively stiff cardboard disc 20, or theequivalent,.is mounted in any suitable manner on the adapter 21. Securedto. the underside of the adapter 21 is a semi-circular element 22provided with three downwardly extending prongs 23. Acylindricalcap-shaped elementor stud 24 is also rigidly mounted on theunder surface of the adapter. The cap 24 and prongs 23 are so positionedthat when the adapter is fitted on the dial 29, the stud fits into theZero hole 26 of the finger wheel25 and the prongs 23 engage the innersurface ofthe fingerholes 30, 31 and 32. The prongs 23 are so formed asto effect a positive engagement of the adapterwiththe finger wheel. Ahandle 33 rigidly mounted on the adapter, is provided as a means formanually rotating the target. The stud is located in the zero hole ofthe finger. wheel in order that the full pulse range of the dial towhich the target was laid out may be obtained. The position of thetarget on the adapter is so chosen that the mark 35 stands convenientlytowards the observer when the dial is fully wound.

When in operation the target is clamped to the finger wheel by means ofthe cap 24 and prongs 23. The observer then grasps a tuning forkpreferably of the'type shown in the copending application, Serial No.378,157, filed July 13, 1929, and sights the target indication 35through the fork tines, which may be partially distended to permit aclear view of the indication 35. Maintaining the fork shown at 36in thisposition, the observer grasps the handle 33 and rotates the finger wheel25 until the cap-shaped element 24 strikes the finger stop 37. The forktines are then actuated and the finger wheel released. On the returnmovement of the dial the two rows of indications may be observed, andany apparent relative movements of the indications will determinewhether or not the dial is operating at the desired condition of speed.Should the outer row of indications appear to stand still the dial willbe operating at its minimum L speed limit, in the present case, eightpulses per second. It the inner row appears to stand still the dial isworking at its maXimum speed, or eleven pulses per second. A clockwisemovement of the inner row of indications and a counter-clockwise movement of the outer row when viewed through the vibrating tines of thefork indicate that the dial is operating at a speed within the twolimits. In observing the dial through the tuning fork 86 the mostaccurate results when the divisions appear to be nearly standing stillare obtained when the fork is held close to the dial and the eye of theobserver at a distance from the sighting aperture in the fork mechanism.At other times the fork may be held for convenience, as shown in Fig. 1.i

What is claimed is:

1. In combination with a rotating body having a nonuniform speed ofrotation, an indicator suitably mounted on said body and bearing aplurality of irregularly spaced indications the size and location ofwhich on the indicator bear a direct relationship to the nonuniformspeed characteristic of said rotating body.

2. In combination, a rotatable body having a non-uniform speed ofrotation, an indicator suitably mounted on said body and bearing aplurality of irregularly spaced indications the size and location ofwhich on the indicator bear a direct relationship to the non-uniformspeed characteristic of said rotating body and means forstroboscopically viewing the indications on the in dicator during therotation thereof.

3. In combination, a rotatable body having a non-uniform speed ofrotation, an indicator mounted on said body and bearing a plurality ofirregularly spaced indications the size of each of which bears a directrelationship to an instantaneous speed value of said rotatable body andeach of said indi cations located on said indicator in such a mannerthat when the indicator is positioned on the rotatable body eachindication may be observed stroboscopically at the instant in which therotatable body is traveling at the instantaneous speed valuecorresponding to the indication observed.

4. In combination with a rotating body having a non-uniform speedcharacteristic, an indicator associated with said rotating body andhaving a plurality of irregularly spaced indications, the sizes of whichbear a relationship to the non-uniform speed characteristic of saidrotating body and means for stroboscopically viewing the indications onthe indicator during rotation of said rotating body.

5.v In combination with a rotatable telephone dial having a non-uniformspeed characteristic, means supported by said dial bearing an annularnon-uniform series of indications rotatable in unison with said dial andmeans for stroboscopically viewing the indications, the size of each ofsaid indications bearing a relationship to an instantaneous speed valueof said non-uniformlyrotatable dial.

In witness whereof, I hereunto subscribe my name this 16th day of April,1930.

' HOWARD BROADVVELL.

